Showing papers on "Demodulation published in 2007"

Survey of automatic modulation classification techniques: classical approaches and new trends

Abstract: The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver, with various civilian and military applications. Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information and so on, blind identification of the modulation is a difficult task. This becomes even more challenging in real-world scenarios with multipath fading, frequency-selective and time-varying channels. With this in mind, the authors provide a comprehensive survey of different modulation recognition techniques in a systematic way. A unified notation is used to bring in together, under the same umbrella, the vast amount of results and classifiers, developed for different modulations. The two general classes of automatic modulation identification algorithms are discussed in detail, which rely on the likelihood function and features of the received signal, respectively. The contributions of numerous articles are summarised in compact forms. This helps the reader to see the main characteristics of each technique. However, in many cases, the results reported in the literature have been obtained under different conditions. So, we have also simulated some major techniques under the same conditions, which allows a fair comparison among different methodologies. Furthermore, new problems that have appeared as a result of emerging wireless technologies are outlined. Finally, open problems and possible directions for future research are briefly discussed.

High-Performance Cooperative Demodulation With Decode-and-Forward Relays

Abstract: Cooperative communication systems using various relay strategies can achieve spatial diversity gains, enhance coverage, and potentially increase capacity. For the practically attractive decode-and-forward (DF) relay strategy, we derive a high-performance low-complexity coherent demodulator at the destination in the form of a weighted combiner. The weights are selected adaptively to account for the quality of both source-relay-destination and source-destination links. Analysis proves that the novel coherent demodulator can achieve the maximum possible diversity, regardless of the underlying constellation. Its error performance tightly bounds that of maximum-likelihood (ML) demodulation, which provably quantifies the diversity gain of ML detection with DF relaying. Simulations corroborate the analysis and compare the performance of the novel decoder with existing diversity-achieving strategies including analog amplify-and-forward and selective-relaying.

Arctangent Demodulation With DC Offset Compensation in Quadrature Doppler Radar Receiver Systems

Abstract: Direct-conversion microwave Doppler radar can be used to detect cardiopulmonary activity at a distance. One challenge for such detection in single channel receivers is demodulation sensitivity to target position, which can be overcome by using a quadrature receiver. This paper presents a mathematical analysis and experimental results demonstrating the effectiveness of arctangent demodulation in quadrature receivers. A particular challenge in this technique is the presence of dc offset resulting from receiver imperfections and clutter reflections, in addition to dc information related to target position and associated phase. These dc components can be large compared to the ac motion-related signal, and thus, cannot simply be included in digitization without adversely affecting resolution. Presented here is a method for calibrating the dc offset while preserving the dc information and capturing the motion-related signal with maximum resolution. Experimental results demonstrate that arctangent demodulation with dc offset compensation results in a significant improvement in heart rate measurement accuracy over quadrature channel selection, with a standard deviation of less than 1 beat/min

Theory and Implementation of an Analog-to-Information Converter using Random Demodulation

Abstract: The new theory of compressive sensing enables direct analog-to-information conversion of compressible signals at sub-Nyquist acquisition rates. The authors develop new theory, algorithms, performance bounds, and a prototype implementation for an analog-to-information converter based on random demodulation. The architecture is particularly apropos for wideband signals that are sparse in the time-frequency plane. End-to-end simulations of a complete transistor-level implementation prove the concept under the effect of circuit nonidealities.

A Passive UHF RF Identification CMOS Tag IC Using Ferroelectric RAM in 0.35- $\mu{\hbox {m}}$ Technology

Abstract: A passive UHF RF identification (RFID) tag IC with embedded 2-KB ferroelectric RAM (FeRAM) for rewritable applications enables a 2.9 times faster read-and-write transaction time over EEPROM-based tag ICs. The resulting FeRAM-based tag has a nominally identical communication range for both read and write operations, which is indispensable for data write applications. The evaluated tag communication range with a folded dipole antenna is from 0 m to 4.3 m, at the 953-MHz carrier frequency with 4-W transmitting Effective Isotropic Radiated Power (EIRP) from a reader/writer. The developed tag IC features two circuit blocks to maximize the communication range in 0.35-mum CMOS/FeRAM technology. First is a CMOS-only full-wave rectifier, which can improve the measured efficiency by up to 36.6% by reducing the input parasitic capacitances and optimization of multiplier structure. This efficiency is more than twice that of previously-published results. Second is a low-voltage current-mode ASK demodulator to accommodate a low-breakdown voltage of FeRAM, which converts the ASK power modulation into a linearly modulated current over an incoming power range of 27 dB, corresponding to the entire communication range. The developed demodulator can thus resolve the primary design tradeoff issue between device protection and detection sensitivity in the conventional voltage-mode demodulator

Compensation of I-Q imbalance in digital transceivers

Abstract: A transceiver includes a switching unit configurable for isolating an input of a receiver from an output of a transmitter during a local calibration mode. A known signal present at the output at a first power level during the calibration mode will also be present at the input at a second power level lower than the first power level and will be converted by the quadrature demodulator. A compensation factor is estimated for compensating the receiver section for imbalances in the in-phase and quadrature phase signals resulting from conversion of the known signal. Remote calibration is implemented using a method for remotely compensating for I-Q imbalance wherein a data packet having a known signal is transmitted to a receiver for conversion by a quadrature demodulator and compensation factors are estimated for compensating for imbalances in the in-phase and quadrature phase signals resulting from conversion of the known signal.

Chaos Applications in Telecommunications

Abstract: Introduction Peter Stavroulakis Chaotic Signal Generation and Transmission Antonio Candido Faleiros,Waldecir Joao Perrella,Tania Nunes Rabello,Adalberto Sampaio Santos, and NeiYoshihiro Soma Chaotic Transceiver Design Arthur Fleming-Dahl Chaos-Based Modulation and Demodulation Techniques Francis CM Lau and Chi K Tse A Chaos Approach to Asynchronous DS-CDMA Systems S Callegari, G Mazzini, R Rovatti, and G Setti Channel Equalization in Chaotic Communication Systems Mahmut Ciftci Optical Communications using Chaotic Techniques Gregory D VanWiggeren APPENDIX A Fundamental Concepts of the Theory of Chaos and Fractals Tassos Bountis APPENDIX B Mathematical Models of Chaos Christos H Skiadas

Near field rf communicators and near field rf communications-enabled devices

Abstract: A near field RF communicator has an antenna circuit (120) to receive a modulated radio frequency signal by inductive coupling and demodulation circuitry (130 or 131) to extract the modulation from a received modulated radio frequency signal inductively coupled to the antenna circuit. The demodulation circuitry has a virtual earth input comprising a current mirror. The demodulation circuitry may be formed by an amplifier (115 or 116) and a demodulator (114) coupled to an output of the amplifier. The amplifier may be a single input amplifier (116) coupled to an output of the antenna circuit or may be a differential amplifier (115) having first and second inputs to receive the modulated radio frequency signal from first and second outputs of the antenna circuit, with each amplifier input providing a virtual earth input.

Individual channel phase delay scheme

Abstract: Embodiments of the present invention are directed to processing an incoming signal by using a demodulation signal, while controlling the phase of the demodulation signal in relation to the incoming signal. The incoming signal can be processed by being mixed with the modulation signal at a mixer. The mixing may thus cause various beneficial modifications of the incoming signal, such as noise suppression of the incoming signal, rectification of the incoming signal, demodulation of the incoming signal, etc.

Carbon nanotube radio.

Abstract: Here we report experimental results for a carbon nanotube (CNT) based amplitude-modulated (AM) demodulator for modulation frequencies up to 100 kHz. Further, the CNT based demodulator was successfully demonstrated in an actual AM radio receiver operating at a carrier frequency of 1 GHz and capable of demodulating high-fidelity audio. The demodulation originates from the nonlinear current−voltage (IDS vs VDS) characteristic of the CNT, which induces rectification of a portion of the applied RF signal. By properly biasing the CNT such that the operating point is centered on the maximum nonlinear portion of the I−V curve, one can maximize the demodulation effect. This represents a simple application of carbon nanotubes and nanotechnology to the wireless realm.

A 2.5 nJ/bit 0.65 V Pulsed UWB Receiver in 90 nm CMOS

Abstract: A noncoherent 0-16.7 Mb/s ultra-wideband (UWB) receiver using 3-5 GHz subbanded pulse-position modulation (PPM) signaling is implemented in a 90 nm CMOS process. The RF and mixed-signal baseband circuits operate at 0.65 V and 0.5 V, respectively. Using duty-cycling, adjustable bandpass filters, and a relative-compare baseband, the receiver achieves 2.5 nJ/bit at 10-3 BER with -99 dBm best case sensitivity at 100 kb/s. The energy efficiency is maintained across three orders of magnitude in data rate. For data rates less than 10 kb/s, leakage power dominates energy/bit.

Data Transmission by FrequencyDivision Multiplexing Using the Discrete Fourier Transform

Abstract: The Fourier transform data communication system is a realization of frequency-division multiplexing (FDM) in which discrete Fourier transforms are computed as part of the modulation and demodulation processes. In addition to eliminating the banks of subcarrier oscillators and coherent demodulators usually required in FDM systems, a completely digital implementation can be built around a special-purpose computer performing the fast Fourier transform. In this paper, the system is described and the effects of linear channel distortion are investigated. Signal design criteria and equalization algorithms are derived and explained. A differential phase modulation scheme is presented that obviates any equalization.

Coherent Optical Phase-Modulation Link

Abstract: We demonstrate and characterize a new class of radio-frequency (RF)-photonic link for the linear transport of analog RF signals. Simultaneous and separate detection and digitization of optical in-phase and quadrature-phase signals is employed for linear phase demodulation in the digital domain. This is shown to allow significantly larger tolerance to imperfect physical implementation of the phase demodulating receiver. Digitizer-limited spur-free dynamic range improvement >12 dBldrHz2/3 is observed in our baseband demonstration. Modulation depths significantly exceeding unity are allowed and demonstrated.

Microring-based modulation and demodulation of DPSK signal.

Abstract: Ultra-small modulator and demodulator for 10 Gb/s differential phase-shift-keying (DPSK), using silicon-based microrings, are proposed. A single-waveguide microring modulator with over-coupling between ring and waveguide generates a DPSK signal, while a double-waveguide microring filter enables balanced DPSK detection. These modulator and demodulator are characterized. A trade-off between pattern dependence of the Duobinary signal and alternate-mark inversion signal power in demodulator design is discussed. Power penalty of the proposed approach is 0.8 dB relative to baseline using conventional modulation and demodulation techniques.

Phase Modulation With Interferometric Detection as an Alternative to Intensity Modulation With Direct Detection for Analog-Photonic Links

Abstract: We analyze the performance of analog-photonic links employing phase modulation with interferometric demodulation and compare it to intensity-modulation direct-detection links. We derive expressions for RF gain, RF noise figure, compression dynamic range, and spurious-free dynamic range for both architectures. We demonstrate theoretically and experimentally that phase-modulated links can outperform intensity-modulated links over substantial frequency ranges.

A Hall Sensor Analog Front End for Current Measurement With Continuous Gain Calibration

Abstract: This paper presents a new technique for continuously calibrating the sensitivity of a current measurement microsystem based on a Hall magnetic field sensor. An integrated reference coil generates a magnetic field for calibration. Using a variant of the chopper modulation, the spinning current technique, combined with a second modulation of the reference signal, the sensitivity of the complete system is continuously measured without interrupting normal operation. Modulation and demodulation schemes allowing the joint processing of both external and reference magnetic fields are proposed. Additional techniques for extracting the very low reference signal are presented. The implementation of the microsystem is then discussed. Finally, measurements validate the calibration principle. A thermal drift lower than 50 ppm/degC is achieved. This is 6-10 times less than in state-of-the-art implementations. Furthermore, the calibration technique also compensates drifts due to mechanical stresses and ageing

Analysis, Optimization, and Implementation of Low-Interference Wireless Multicarrier Systems

Abstract: This paper considers pulse-shaping multicarrier (MC) systems that transmit over doubly dispersive fading channels. We provide exact and approximate expressions for the intersymbol and intercarrier interference occurring, in such systems. This analysis reveals that the time and frequency concentration of the transmit and receive pulses is of paramount importance for low interference. We prove the (nonobvious) existence of such jointly concentrated pulse pairs by adapting recent mathematical results on Weyl-Heisenberg frames to the MC context. Furthermore, pulse optimization procedures are proposed that aim at low interference and capitalize on the design freedom existing for redundant MC systems. Finally, we present efficient FFT-based modulator and demodulator implementations. Our numerical results demonstrate that for realistic system and channel parameters, optimized pulse-shaping MC systems can outperform conventional cyclic-prefix OFDM systems

Receiver and integrated AM-FM/IQ demodulators for gigabit-rate data detection

Abstract: Provision of gigabit-rate data transmission over wireless radio links, using carrier frequencies in the millimeter-wave range (>30 GHz). More specifically, a circuit for detection of amplitude-shift keyed (ASK) or other amplitude modulations (AM) which can be easily incorporated into an integrated circuit receiver system is described, making the receiver capable of supporting both complex IQ modulation schemes and simpler, non-coherent on-off or multiple-level keying signals. Several novel radio architectures are also described which, with the addition of a frequency discriminator network, have the capability of handling frequency shift keyed (FSK) or other frequency modulations (FM), as well as AM and complex IQ modulation schemes. These radio architectures support this wide variety of modulations by efficiently sharing detector hardware components. Disclosed herein are architecture for supporting both quadrature down-conversion and ASK/AM, ASK/AM detector circuit details, AM-FM detector architecture, and an AM-FM/IQ demodulator system and FSK/FM detector circuit details.

A 900 MHz UHF RFID Reader Transceiver IC

Abstract: The proliferation of RFID applications motivates an integrated solution to reduce the cost and physical size of readers. This paper describes the architecture and design of a world-wide regulation-compliant single-chip RFID transceiver for multiclass tags. Based on direct-conversion architecture, this chip integrates all of the RF blocks, synthesizer, analog signal conditioning, ADC/ DAC, and modulation and demodulation functions. Fabricated on a 0.18 mum SiGe BiCMOS process, this chip occupies 21 mm2 and produces output power of +11 dBm in linear mode and +20 dBm under supply modulation mode; the receiver has sensitivity down to -85 dBm in the presence of a 0 dBm self-jammer signal. Total power consumption is 1.2 W.

35–65-GHz CMOS Broadband Modulator and Demodulator With Sub-Harmonic Pumping for MMW Wireless Gigabit Applications

Abstract: Sub-harmonic modulator and demodulator are presented in this paper using 0.13-mum standard CMOS technology for millimeter-wave (MMW) wireless gigabit direct-conversion systems. To overcome the main problem of local oscillator (LO) leakage in direct-conversion systems, the sub-harmonically pumped scheme is selected in this mixer design. An embedded four-way quadrature divider is utilized in the sub-harmonic Gilbert-cell design to generate quadrature-phases LO signals at MMW frequency. For broadband applications, a broadband matching design formula is provided in this paper to extend the operational frequency range from 35 to 65 GHz. To improve the flatness of conversion loss at high frequency, high-impedance compensation lines are incorporated between the transconductance stage and LO switching quad of the Gilbert-cell mixer to compensate the parasitic capacitance. The sub-harmonic modulator and demodulator exhibit 6 plusmn1.5 dB and 7.5 plusmn1.5 dB measured conversion loss, respectively, from 35 to 65 GHz. For MMW wireless gigabit applications, the gigabit modulation signal test is successfully performed through the direct-conversion system in this paper. To our knowledge, this is the first demonstration of the MMW CMOS sub-harmonic modulator and demodulator that feature broadband and gigabit applications.

Reduced-complexity UWB time-reversal techniques and experimental results

Abstract: This paper presents a reduced-complexity time reversal technique for ultra-wideband (UWB) communications. Time reversal takes advantage of rich scattering environments to achieve signal focusing via transmitter-side processing, which enables the use of simple receivers. The goal of this paper is to demonstrate a UWB time reversal system architecture based on experimental results and practical pulse waveform, taking into account some practical constraints, and to show feasibility of UWB time reversal. Pre-decorrelating in addition to time reversal processing is considered for a downlink multiuser configuration. Multiple transmit antennas are employed to improve the performance.

Digitally enhanced heterodyne interferometry

Abstract: Combining conventional interferometry with digital modulation allows interferometric signals to be isolated based on their delay. This isolation capability can be exploited in two ways. First, it can improve measurement sensitivity by reducing contamination by spurious interference. Second, it allows multiple optical components to be measured using a single metrology system. Digitally enhanced interferometry employs a pseudorandom noise (PRN) code phase modulated onto the light source. Individual reflections are isolated based on their respective delays by demodulation with the PRN code with a matching delay. The properties of the PRN code determine the degree of isolation while preserving the full interferometric sensitivity determined by the optical wavelength. Analysis and simulation indicate that errors caused by spurious interference can be reduced by a factor inversely proportional to the PRN code length.

Mis-Matched Modulation-Demodulation Format Selectable Filters

Abstract: Modulation-demodulation format selectable (MFS) processor, cross-correlator and transmit filter for processing, cross-correlating and filtering in-phase and quadrature-phase baseband signal and providing a first bit rate and a second bit rate baseband signal to a modulator and a transmitter for modulation and transmission of the processed filtered baseband signal. Transmit amplifier operated in a first radio frequency (RF) band for amplification of the first bit rate modulated signal and a second RF amplifier operated in a second RF band for amplification of the second bit rate modulated signal. Switch for selecting the first or the second bit rate or first or second modulation format signal and providing selected signal to a transmitter. Receiver for receiving transmitted signal. Demodulator and demodulator filter mis-matched to transmit baseband filter. Receive processor for receiving and processing quadrature demodulator demodulated baseband filtered signal and for providing first and second format cross-correlated in-phase and quadrature-phase baseband signal. Time division multiplex (TDM) and Orthogonal Frequency Division Multiplex (OFDM) processor and transmit baseband filter for processing, filtering and providing TDM and OFDM processed and filtered signal to a modulator, transmitter and receiver. Receiver and demodulator for demodulating and baseband filtering received modulated TDM signal. Demodulator of TDM signal has a demodulator baseband filter which is mis-matched to the transmit baseband filter and provides demodulated baseband mis-matched filtered cross-correlated in-phase and quadrature-phase signal.

A 1.5-V 0.7–2.5-GHz CMOS Quadrature Demodulator for Multiband Direct-Conversion Receivers

Abstract: An integrated quadrature demodulator with an on-chip frequency divider is reported. The mixer consists of a transconductance stage, a passive current switching stage, and an operational amplifier output stage. A complementary input architecture has been used to increase the transconductance for a given bias current. The circuit is inductorless and is capable of operating over a broad frequency range. The chip was implemented in a 0.13-mum CMOS technology. From 700 MHz to 2.5 GHz, the demodulator achieves 35 dB of conversion voltage gain with 250-kHz IF bandwidth, a double-sideband NF of 10 dB with 9-33 kHz 1/f-noise corner. The measured IIP3 is 4 dBm for a 0.1-MHz IF frequency and 10 dBm for a 1-MHz IF frequency. The total chip draws 20 to 24 mA from a single 1.5-V supply.

Limiting audible noise introduction through FM antenna tuning

Abstract: An FM receiver including an FM antenna that receives continuous wavelength signals, where the FM receiver is coupled to the FM antenna and operable to alter a center frequency of a gain profile of the FM antenna. The FM receiver includes a low noise amplifier module that is coupled to amplify the continuous wavelength signal to produce an amplified RF signal therefrom. A down conversion module is coupled to mix the amplified RF signal with a local oscillation to produce an information signal. A filter module is coupled to filter the information signal to produce a filtered information signal. A demodulation module is coupled to capture audio information from the filtered information signal. A signal monitoring module is coupled to monitor the FM signal quality of a received continuous wavelength signal. The signal monitoring module produces a signal quality indication therefrom. An antenna control module produces a signal value based upon the signal quality indication, wherein the signal value operates to alter the center frequency of a gain profile of the FM antenna.

Diversity wireless systems

Abstract: Diversity wireless system, processor, cross-correlator, transmit baseband filter and modulator for processing, cross-correlating, filtering, modulating and providing a first and a second bit rate signal to a transmission system for transmission of the processed, filtered, modulated signal. Transmission system having two transmitters for transmission of the modulated signal. Diversity receiver system with two receivers for receiving the transmitted modulated signal and for providing received signal to a demodulator. Demodulator, receive baseband filter and receive processor for demodulation, filtering and processing received signal. Receive baseband filter for filtering is mis-matched to the transmit baseband filter for filtering of the first bit rate signal and receive processor for processing first bit rate demodulated baseband filtered signal provides received baseband mis-match filtered cross-correlated in-phase and quadrature-phase signal. Processor and transmit baseband filter for processing and filtering a signal into a cross-correlated filtered and into a cross-correlated spread spectrum in-phase and quadrature-phase baseband signal. Processor, first and second modulator for processing and baseband filtering a signal into time division multiplexed (TDM) filtered signal and into Orthogonal Frequency Division Multiplexed (OFDM) signal and for providing processed TDM filtered and processed OFDM signal to two modulators for modulation, transmission and diversity reception.

Pseudonoise Optical Modulation for Real-Time 3-D Imaging With Minimum Interference

Abstract: In optical time-of-flight (TOF) range imaging, harmonic intensity modulation of the illumination source is very common. By detecting the phase delay between emitted and reflected sinusoids, the distance can be measured accurately. However, this harmonic approach does not allow for the concurrent operation of several TOF range cameras because the arbitrary superposition of several differently parametrized sinusoids leads to a sinusoid with incorrect phase. To minimize inaccuracies by multi-camera interference (MCI), pseudonoise (PN) modulated intensity signals are employed for robust TOF range imaging. The time of flight is locally measured by correlating the incident light intensity with two time-shifted versions of the PN sequence, making use of smart demodulation pixels. We derive two fundamental expressions for the basic limitations of TOF measurements using PN sequences. Firstly, the precision of the distance measurement is limited by photon shot noise, and it essentially shows an inverse square root dependence of the number of detected photoelectrons. Secondly, MCI causes an inaccurate distance measurement given as the ratio of two sums. The denominator is the sum of two autocorrelation and two cross-correlation values; the nominator is the sum of one autocorrelation and one cross-correlation value. Due to the lack of a strict mathematical theory of correlation properties of m-sequences, an exhaustive numerical simulation was carried out to obtain expectation values of the distance measurement inaccuracy as a function of the sequence length and the number of interfering cameras. For experimental verification, an image sensor with 176 times 144 demodulation pixels was manufactured with a standard CMOS process offering a CCD option. Measurements taken with up to five concurrently operating sensors were in excellent agreement with our theoretical predictions concerning achievable distance accuracy. This confirms the aptness of PN techniques for multi-camera optical TOF range imaging.

Bluetooth,internet,multimode TDMA, GSM, spread spectrum, CDMA

Abstract: Bluetooth transmitter and receiver for transmitting and receiving voice signal and for providing received voice signal to a processor for processing demodulated Bluetooth signal. Location finding signal receiver, demodulator and processor for receiving, demodulating and processing a location finder signal into demodulated processed location finder signal and for processing location finder signal with processed and filtered Time Division Multiple Access (TDMA) signal, or with processed and filtered cross-correlated in-phase and quadrature-phase signal, or with processed Orthogonal Frequency Division Multiplexed (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA) or with spread spectrum Code Division Multiple Access (CDMA) signal. Modulator and transmitter for modulation and transmission of processed signal. Receiver for receiving transmitted signal. Demodulator, receiver filter and receiver processor for demodulation, filtering and processing of received modulated cross-correlated signal having filter for filtering of the cross-correlated signal which is mismatched to the transmit filter of the cross-correlated signal. Receive processor provides received mis-match filtered cross-correlated in-phase and quadrature-phase signal. Location finder signal received from one or more satellites and from one or more ground based single or plurality of transmitters. Receiver for receiving transmitted signal has a radio frequency (RF) unit which is located at a remote location from demodulator. OFDM or OFDMA signal is used in a Wireless Local Area Network (WLAN) or a Wi-Fi network and TDMA signal in a cellular network.

Adaptive controller for linearization of transmitter with impairments

Abstract: An adaptive controller for linearization of transmitters using predistortion of the input signal has reduced sensitivity to impairments such as gain variation, phase noise or modulation/demodulation frequency instability by linearizing an adaptively normalized gain provided through a separate estimation and cancellation of linear gain variations. Values of a nonlinear and a linear gain blocks, cascaded with the linearized transmitter and called respectively a predistortion block and a gain regulation block, are independently adjusted by two different adaptive controllers. In one embodiment, four banks of real gain elements compose the predistortion block and realize an arbitrary step-wise approximation of a generalized 2×2 transmit gain matrix of nonlinear functions. In a further embodiment cancellation of a DC level bias multi-channel impairment is provided by an adaptively adjusted signal adder inserted in the transmit chain between the predistortion block and the linearized transmitter.